Fix VideoFromComponents.save_to crash when writing to BytesIO (Comfy-Org#12683)

* Fix VideoFromComponents.save_to crash when writing to BytesIO

When `get_container_format()` or `get_stream_source()` is called on a
tensor-based video (VideoFromComponents), it calls `save_to(BytesIO())`.
Since BytesIO has no file extension, `av.open` can't infer the output
format and throws `ValueError: Could not determine output format`.

The sibling class `VideoFromFile` already handles this correctly via
`get_open_write_kwargs()`, which detects BytesIO and sets the format
explicitly. `VideoFromComponents` just never got the same treatment.

This surfaces when any downstream node validates the container format
of a tensor-based video, like TopazVideoEnhance or any node that calls
`validate_container_format_is_mp4()`.

Three-line fix in `comfy_api/latest/_input_impl/video_types.py`.

* Add docstring to save_to to satisfy CI coverage check

Author: artokun

comfy_api/latest/_input_impl/video_types.py

@@ -401,13 +401,18 @@ def save_to(
         codec: VideoCodec = VideoCodec.AUTO,
         metadata: Optional[dict] = None,
     ):
+        """Save the video to a file path or BytesIO buffer."""
         if format != VideoContainer.AUTO and format != VideoContainer.MP4:
             raise ValueError("Only MP4 format is supported for now")
         if codec != VideoCodec.AUTO and codec != VideoCodec.H264:
             raise ValueError("Only H264 codec is supported for now")
         extra_kwargs = {}
         if isinstance(format, VideoContainer) and format != VideoContainer.AUTO:
             extra_kwargs["format"] = format.value
+        elif isinstance(path, io.BytesIO):
+            # BytesIO has no file extension, so av.open can't infer the format.
+            # Default to mp4 since that's the only supported format anyway.
+            extra_kwargs["format"] = "mp4"
         with av.open(path, mode='w', options={'movflags': 'use_metadata_tags'}, **extra_kwargs) as output:
             # Add metadata before writing any streams
             if metadata is not None: